The present invention mainly relates to an optical transmission module for use in an optical transmission system or an optical exchange system, and in particular relates to an optical coupling technology, such as an optical wave-guide, a light-beam spot converter and so on, for obtaining an optical coupling with a high efficiency, for instance, between a light emitting or light receiving element and an optical fiber, a light emitting or light receiving element and an optical circuit in the optical transmission module, and/or between the optical circuit and the optical fiber, as well as for obtaining easy install and manufacture thereof.
With development of an optical information transmission path or network, a plan of applying an information transmission with use of an optical fiber was made, not only for use in a business building for various industries, but also into a condominium and/or a separated house or building. One of the important problems therein, needless to say, but is in lowering of a price for such the optical transmission system, in particular the lowering of the price of the optical transmission module, which is connected to a general subscriber at a terminal. For the purpose of great reduction of the cost of the optical transmission module for the subscriber, in recent years, an attempt was made of putting a semiconductor laser having a converter of a light beam-spot diameter into practical use. This is an attempt to aim the low cost of it by means of a method for mounting an optical device(s) or element(s) on a single or a one flat surface and of removal of lenses, and can be understood or interpreted to let the semiconductor laser to own a lens function by itself, so as to remove the lens therefrom. This converter of the light beam-spot diameter, i.e., as a magnifier for the light beam-spot diameter, does not necessarily have a sufficient performance or power in the lens function, however the light beam after emission is narrowed in an extent thereof, thereby improving the optical coupling directly to the optical fiber, or the like, comparing to that of the laser device of the conventional type. As a result of this, the optical module can be assembled with ease and the mounting thereof also can be simplified, thereby advancing the attempt of the reduction in manufacturing cost by a one step.